Image: ESO
AIMING HIGH. An 8-meter telescope at Cerro Paranal in Chile began recording its first scientific data on the night of May 25. Formidable in its own right, the telescope comprises only one quarter of the planned observatory, scheduled for completion in 2003.
On the cold, cloudless night of May 25 in a remote desert in Chile, a huge protective enclosure slid open, exposing a giant telescope to the dim light of distant stars and galaxies. As the faint illumination reflected onto its gleaming, newly-coated mirror, 8.2 meters in diameter, the instrument began collecting its first scientific data--a once-in-a-telescope event that astronomers call "First Light."

A day later, elated astronomers from the European Southern Observatory, a 10-nation consortium that is building the new observatory, marked the event at ESO headquarters in Garching, Germany and at nine other sites in member countries by releasing the first images recorded by the new telescope--the first of four that are being constructed at the site. "Even at this very early stage of evaluation we can state with confidence that the technical performance of the first 8-meter telescope meets or exceeds our expectations in all respects," said ESO General Director Riccardo Giacconi in an address from Garching.

The new telescope at Cerro Paranal is the cornerstone of an ambitious program by European nations to reclaim a leadership in optical astronomy that they held from the time of Galileo. When it is completed in 2003, the four-telescope array, known as the VLT (for Very Large Telescope), will comprise the world's most powerful ground based optical and infrared observatory. Its ability to resolve distant objects will rival--and sometimes exceed--telescopes in space, such as the U.S. Hubble Space Telescope. "For Europe this marks the realization for the first time in this century of a facility for ground based optical and infrared astronomy which equals or surpasses any available in the world," Giacconi said.


Planning for the VLT began in the late 1970s and the project moved into full swing in December 1987. The final step in preparing the first unit was the application of a thin coating of aluminum on the mirror, measuring 8.2 meters in diameter. The only larger mirror is the 10-meter telescope at the U.S. Keck Observatory on Mauna Kea, Hawaii. The coating operation, in a huge vacuum chamber, was completed at Paranal on May 20 and the mirror was installed in the telescope housing on May 21. A series of tests on the instrument's tracking and resolving ability were conducted over the next four days, leading up to the First Light on May 25.

The planned observatory incorporates advanced technology that will make it the most sophisticated ever built. The main glass mirrors, cast according to a thin honeycomb design, rest on a system of 150 computer-controlled actuators that can bend them slightly to induce precise distortions. This system, known as active optics, allows operators to adjust the lens to compensate for aberrations that would distort images. A second set of smaller mirrors--which reflect the light to viewing and recording instruments--is also computer controlled.

Astronomers will be able to combine the light from the four telescopes, once completed, into a single image, producing the equivalent of a telescope with a mirror 16 meters in diameter. And they have still another trick up their sleeves; the telescope array is designed to function as an interferometer--a device that combines the wave patterns of light from the various telescopes. A number of such projects, believed to be the cutting edge of optical astronomy, are underway around the world.

The result of using several telescopes as an interferometer is a "virtual mirror" 100 meters or more in diameter. This technique will provide the VLT--the biggest so far--with unparalleled resolving power of distant objects in the cosmos. "This is likely to remain the highest angular resolution achieved by humankind for quite a while or at least until we can figure out how to do this from space with individual telescope separations of hundreds of kilometers," Francesco Paresce, a VLT project scientist told Scientific American.

Data from the telescope is transmitted through a dedicated satellite link to the ESO headquarters in Germany, where it is interpreted and archived.


The European's have already picked their targets. The VLT will be used to search for planets orbiting distant stars, to study star formation and early stellar evolution and to monitor stellar surface structures. It will also be able to probe the innards of our own home galaxy, the Milky Way.


Although a great deal of work must before the entire installation is complete, the few images released so far have already convinced many astronomers that Paranal may outshine many of the famous Earth observatories. Tests showed that the telescope had the right stuff in its ability to image faint and distant objects and to pick up fine details never before achieved with any ground-based telescope.

The commissioning and science verification phases of the complex facility will last until April 1, 1999. From then on, the facility will be open to the investigations of visiting astronomers. If seeing is believing, we can expect a series of new discoveries that will rival the recent successes of the Hubble and the Keck.